This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:                3GPP third generation partnership project        AP access point        BW bandwidth        CA carrier aggregation        CC component carrier        CCA clear channel assessment        CE control element        DL downlink (eNB towards UE)        DS direct sequence        eNB E-UTRAN Node B (evolved Node B)        E-UTRAN evolved UTRAN (LTE)        FH frequency hopping        ISM industrial scientific medical        LTE long term evolution of UTRAN (E-UTRAN)        LTE-A long term evolution advanced        MAC medium access control        MTC machine type communication        Node B base station        OFDM orthogonal frequency division multiplexing        PCC primary cell carrier        PCFICH physical control format indicator channel        PDCCH physical downlink control channel        PHICH physical hybrid indicator channel        PHY physical        PRB physical resource block        PUCCH physical uplink control channel        RRC radio resource control        SCC secondary cell carrier        UE user equipment, such as a mobile station or mobile terminal        UL uplink (UE towards eNB)        
As is specified in 3GPP documents, LTE-A should operate in spectrum allocations of different sizes, including wider spectrum allocations than those of prior LTE releases (e.g., up to 100 MHz) to achieve the peak data rate of 100 Mbit/s for high mobility and 1 Gbit/s for low mobility. Carrier aggregation, where two or more component carriers (CCs) are aggregated, may be used in order to support transmission bandwidths larger than 20 MHz. The carrier aggregation could be contiguous or non-contiguous. This technique, as a bandwidth extension, can provide significant gains in terms of peak data rate and cell throughput as compared to non-aggregated operation.
A terminal may simultaneously receive one or multiple component carriers depending on its capabilities. A LTE-A terminal with reception capability beyond 20 MHz can simultaneously receive transmissions on multiple component carriers. A legacy terminal might receive transmissions on a single component carrier only, provided that the structure of the component carrier follows the relevant specifications. Moreover, it is required that LTE-A should be backwards compatible with older standards in the sense that a legacy terminal should be operable in the LTE-A system, and that a LTE-A terminal should be operable in a Rel-8 LTE system.
FIG. 1 shows an example of the carrier aggregation, where M 20 MHz component carriers are combined together to form M×20 MHz BW (e.g., 5×20 MHz=100 MHz given M=5). Legacy terminals may receive/transmit on one component carrier, whereas LTE-A terminals may receive/transmit on multiple component carriers simultaneously to achieve higher (wider) bandwidths.
With further regard to carrier aggregation, what is implied is that one access point (e.g., an eNB) can effectively contain more than one cell on more than one CC (frequency carrier), and the eNB can utilize one (as in E-UTRAN Rel-8) or more cells (in an aggregated manner) when assigning resources and scheduling the UE.
Carrier aggregation (CA) in LTE-Advanced extends the maximum bandwidth in the uplink (UL) or downlink (DL) directions by aggregating multiple carriers within a frequency band (intra-band CA) or across frequency bands (inter-band CA).
A primary cell carrier (PCC) using LTE technology may be configured on a licensed band for primary access in order to provide mobility, security and state management for user terminals while a secondary cell carrier (SCC) (e.g., using WLAN technology) is opportunistically configured/activated on an un-licensed band for secondary access. The SCC may be used to provide additional data plane transport.
As many machine type communication (MTC) devices are targeting for low-end applications (e.g., low cost, low data rate, etc.) which can be handled adequately by GSM/GPRS. However, MTC device vendors and operators may wish to consider migrating low-end MTC devices from GSM/GPRS to LTE networks. This move may provide benefits for reducing radio frequency (RF) component cost in the devices, for example, simplification and reduction in support of bands/radio access technologies (RAT)/RF chains/antenna ports, transmission power, lower maximum channel bandwidths for various frequency bands, and support of half-duplex FDD mode. Additionally, benefits may be gained due to baseband-RF conversion aspects, significantly lower peak data rate support, less required support of spatial processing mode in uplink/downlink and reduced radio protocol processing.
Frame based requirements in “Listen Before Talk” applications which may be based on “Detect and Avoid” strategies may not apply to a transmission equipment if it limits its max output power (e.g., to 10 dBm instead of the 20 dBm/23 dBm max output power, such as specified in the ISM 2.4 GHz/5 GHz unlicensed bands). Thus, before transmission, the equipment might not need to perform a clear channel assessment (CCA) in order to check using energy detection; observe the operating channel for the duration of the CCA observation time (e.g., 20 μs min); consider a channel to be occupied if the energy level in the channel exceeds the energy detection threshold or, if the channel is clear, begin transmitting immediately. This significantly facilitates the deployment of LTE on un-licensed band as the LTE transmitter may transmits without a need for sensing of WiFi transmissions provided it limits its transmission power to 10 dBm.
A standalone LTE system operating in an un-licensed band may use some intra-band carrier aggregation mechanisms to increase robustness against interference from WiFi systems (and from other cellular networks). In carrier aggregation mechanisms, the PCC may be mapped to a carrier, C1, in the un-licensed band, and the SCC may be mapped to another carrier, C2, in the un-licensed band. However, carrier aggregation typically involves more complex RF chain design and more complex baseband-RF conversion aspects. Low-cost MTC devices supported by a standalone LTE system may only have one single Rx chain and baseband processing capability only sufficient to process one carrier at a time which prevents conventional CA techniques where monitoring bother C1 and C2 may be required.
There are up to 3 non-overlapping WiFi channels possible on the ISM 2.4 GHz band if the DS PHY signal is spread over 22 MHz (as in IEEE 802.11b standards); or up to 8 (non-overlapping) channels on the ISM 5 GHz band if using OFDM PHY signals (effectively occupying 16.25 MHz per OFDM signal as in IEEE 802.11a standards). At least two relatively interference-free carriers may be needed for carrier aggregation, which may be difficult to find on the ISM band.
Traditional CA-based solutions for standalone LTE system over the un-licensed band have at least two carriers for the carrier aggregation with some sensing-based protocols (e.g., ON-OFF patterns, CCA), fast CC configuration activation, and broken-CC repair mechanisms. These ways assume the PCC and SCC are active and hence require the UE RF front end and baseband processing to support two carriers at the same time in normal operations. Accordingly, these techniques are not applicable for low-cost MTC devices equipped with a single Rx chain.
There is need for a CA solution that can be both (i) supported by low-cost MTC devices equipped with a single receiver (Rx) chain and limited baseband processing capability, and (ii) deployed in unlicensed band where there may be scarcity of available interference-free carriers.